Electronic article surveillance systems have been used for many years as a means of deterring retail shoplifting in clothing stores, electronic stores, and a myriad of other retail establishments. Generally speaking, an EAS system will begin with a tag, consisting of a durable and reliable, yet small, sensor tag which is affixed to the article to be detected in such a way that it cannot be easily removed by a customer in the store. Usually, the system depends upon the feature that the attachment mechanism is constructed such that it can only be removed by the use of a specialized tool which is only in the possession of the store personnel at the checkout register or exit port for the establishment. In the event that an EAS tag is not removed from a protected article prior to exiting the store, an alarm or other signal is activated.
In many commercially available EAS systems, one or more antennas are placed at the exits and entrances to the retail location. These antennas set up zones, sometimes referred to as interrogation zones, in which an EAS tag (or marker) may be sensed. At least one antenna serves the function of sending out what is called an interrogation signal. The markers on the merchandise are affected by this signal and will respond with a signal of their own. Either the same antenna that sends out the interrogation signal or other additional antennas can sense the signals from the markers. The most effective way to do this is by stopping the broadcast of the interrogation signal to listen for the signals emanating from the markers. If a marker is sensed within the zone created by the antennas, it is presumed that an article is being removed without purchase, and alarms are set off. These alarms may be audible alarms for general broadcast or the alarms may be silent alarms in the form of a light at a check-out counter or security station, etc.
In order to make an EAS system effective, one must consider how to make the EAS tags tamper resistant. This is an on-going effort, because over time, thieves become more clever in learning how to tamper with an EAS tag such as to defeat it. The retailer (and the tag manufacturer) must consider how to detect and prevent tampering with the tags. The particular construction of a tag will determine how tampering is detected.